The typical vehicle brake apply system includes a hydraulic master cylinder that has a fluid link to the wheel brakes and that provides the pressure apply and release mechanism for actuating the wheel brakes in response to the manual application of force to a brake pedal. Generally, a power booster is employed to intensify the force exerted by the driver, and to apply the intensified force to the master cylinder. The majority of power boosters operate on the pressure differential that exists between the engine intake developed vacuum and atmospheric pressure. In some applications the engine's vacuum is augmented with an ancillary pumping device.
As an optional device that doesn't require an engine vacuum source, or in an effort to make power boosters smaller, and/or capable of developing greater input force intensification, hydraulic and pneumatic operating power boosters have been used. An example of a hydraulic power booster is disclosed in U.S. Pat. No. 4,181,064 to Flory, which is assigned to the assignee of this invention. An example of a pneumatic power booster is disclosed in U.S. Pat. No. 5,031,404 to Flory, et al, which is also assigned to the assignee of this invention. That pneumatic booster includes a housing with a pair of flexible diaphragms spaced away from one another and forming a pair of sealed chambers within the housing. A power piston for connection with the master cylinder, a chamber valve seat that separates the chambers, a spring biased control valve and a pedal linkage are all slidably carried within the housing. Movement of a control valve by the pedal linkage operates to apply air pressure to the diaphragms which apply force to the power piston and the master cylinder.
While this prior art pneumatic power booster provides a complete and operationally advantageous unit, manufacturability improvements and cost reductions are continuously desirable. Accordingly, a new pneumatic power booster is sought.